Frequently, overfilled arch structures formed of precast or cast-in-place reinforced concrete are used in the case of bridges to support one pathway over a second pathway, which can be a waterway, a traffic route, or in the case of other structures, a storage space or the like. The terms “overfilled arch” or “overfilled bridge” will be understood from the teaching of the present disclosure, and in general as used herein, an overfilled bridge or an overfilled arch is a bridge formed of arch elements that rest on the ground or on a foundation and has soil or the like resting thereon and thereabout to support and stabilize the structure and in the case of a bridge provide the surface of the second pathway. The arch form is generally arcuate such as cylindrical in circumferential shape, and in particular a prolate shape; however, other shapes can be used. Examples of overfilled bridges are disclosed in U.S. Pat. Nos. 3,482,406 and 4,458,457, the disclosures of which are incorporated herein by reference.
Presently, reinforced concrete overfilled arches are usually constructed by either casting the arch in place or placing precast elements, or a combination of these. These arched structures rest on prepared foundations at the bottom of both sides of the arch. The fill material, at the sides of the arch (backfill material) serves to diminish the outward displacements of the structure when the structure is loaded from above. As used herein, the term “soil” is intended to refer to the normal soil, which can be backfill or in situ, located at a site used for a bridge structure, and which would not otherwise adequately support an arch. The terms “backfill,” and “in situ” will be used to mean such “soil” as well.
Soil is not mechanically strong enough to adequately support bridge structures of interest to this invention. Thus, prior art bridge structures have been constructed to transfer forces associated with the structure to walls of the structure and/or large concrete foundations at the base of the wall. Such walls have to be constructed in a manner that will support such forces and thus have special construction requirements. As will be discussed below, such requirements present drawbacks and disadvantages to such prior art structures.
For the prior art structures, the overfilled arches are normally formed such that the foundation level of the arch is at the approximate level of a lower pathway or floor surface of an underground structure over which the arch spans. Referring to FIGS. 1A-1C, it can be understood that prior art systems S1 and S2 include sides or sidewalls SW1 and SW2 which transfer loads from tops T1 and T2 of the arch to foundation F1 and F2. The sides of arch systems S1 and S2 must be sufficiently thick and contain sufficient reinforcement in order to be able to carry these loads and the thereby induced bending moments.
Furthermore, as it is necessary to limit the arch loading and bending actions in the top and sides of prior art overfilled arch systems to an acceptable level, the radius of the arch is in practice restricted. This restriction in arch radius leads to a higher “rise” R1 and R2 (vertical dimension between the top of clearance profile C1 and C2 of lower pathway surface LS1 or LS2 and crown CR1 and CR2 of the arch) in the arch profile than is often desirable for the economical and practical arrangement of the two pathways and formation of the works surrounding and covering the arch. This results in a lost height LH1 and LH2 which can be substantial in some cases.
Beams or slabs, while needing a larger thickness than arches, do not require this “rise” and, therefore, can be used for bridges accommodating a smaller height between the top of the clearance profile of the lower pathway and the top of the upper pathway. Arches, despite their economical advantage, often cannot compete with structures using beams or slabs for this reason especially for larger spans. However, the larger thickness may result in an expensive structure whose precast elements may be difficult unwieldy and heavy to transport to a building site. Thus, many of the advantages of this structure may be offset or vitiated.
Furthermore, as indicated in FIGS. 1A-1C, foundations F1 and F2 for the prior art overfilled arch systems must be substantial in order to carry the arch loading indicated in FIG. 1C as AL, and require additional excavation at the base of the arch (generally beneath the lower pathway) to enable their construction. As will be understood from the present disclosure, forces AL can be considered as being circumferential forces, and forces AV can be considered as being vertical forces with forces AH being considered as horizontal forces. Loading forces on the system are a combination of these forces.
For overfilled arches made of precast construction, the incorporation of the required height of the sides or sidewalls of the arch result either in a tall-standing precast element which is difficult and unwieldy to transport and to place or in the requirement of pedestals, such as pedestals F1a shown in FIG. 1A.